This invention relates to a method of detecting failure to tighten screws against works and a device therefor, suitable for preventing occurrence of failure to tighten the screws in working step for tightening the screws against the works.
In an assembly line for electrical equipments, for example, various parts are mounted on an electrical equipment body as work by means of screws in a plurality of working steps. Generally, a worker in charge for each step tightens the previously allotted number of screws against each electrical equipment body sequentially conveyed along the assembly line with a tool such as an electric screwdriver or pneumatic screwdriver.
Whether or not the screws are correctly tightened against each work depends upon the degree of skillfulness and carefulness of the worker. Accordingly, it is inevitable that the failure to tighten the screws occurs at a certain rate. Particularly, various types of one electrical equipment have recently been produced in a small number in order that a diversity of consumers' needs can be met. In such circumstances, the number of screws to be used differs from one type of the electrical equipment to another and positions where the screws are tightened are changed with design changes even in one type. Accordingly, contents of work in the screw tightening step are also changed at relatively short intervals. Consequently, the workers cannot sometimes cope with the changes in the work contents, which has caused frequent occurrence of failure to tighten the screws. Conventionally, the products are checked in a final inspection at the assembly line. However, the products are visually inspected, which inevitably causes oversight.